The instant disclosure relates to a seat portion structure for a ground-based hydraulic turbine engine. The seat portion structure includes a base plate. A first bearing element is connected to the base plate and contacts the ground. At least three arms are connected to the base plate by a pivoting link. The arms are adapted for pivoting relative to the base plate between a first position, in which the arms are placed near each other, and a second position, in which the arms radially extend from the base plate. A second bearing element is connected to one end of each arm and contacts the ground. A positioning device is adapted for changing the distance between the end of at least one arm and the associated second element. The structure includes, for each arm, a device for locking the arm in the second position.